Principles and applications of droplet formation in porous-wall channels

Droplets play a fundamental role in a large variety of fields such as pharmaceutics, food technology or chemical processing. These can be used as templates for production of polymeric spheres or capsules, as part of unit operation like liquid-liquid extraction or for cell encapsulation and drug delivery. Particularly when droplets act as templates, the control of size, shape and size distribution is paramount to ensure product quality. A new technology for droplet generation taking advantage of porous-wall channels addresses these requirements. The method as presented in this thesis consists of a porous-wall channel, either as a hollow-fiber membrane or as an embedded channel in a porous flat-sheet membrane. Within these channels, two immiscible phases are brought in contact as coflowing streams and the liquid filament of the inner phase breaks up in the form of droplets either in a dripping or a jetting regime depending on the dominating forces. This is demonstrated both experimentally and with the help of CFD simulations that are able to depict the droplet formation mechanics occurring within the channels. In addition to the study of the principle behind droplet break-up, a design for the generation of droplets at low micron ranges is presented. Furthermore, the potential of this technology is investigated for different applications of commercially available hollow-fiber membranes in the generation of aqueous two-phases systems (ATPS) droplets, droplet solidification, formation of elongated particles, and liquid-liquid extraction, being the latter the one showing most promising results.